Hold the shift key down (or rapidly tap it) when beginning to boot Basilisk II up. You should see a message stating that the extensions are off. Once you get to the Macintosh desktop, go into the System Folder's Extentions folder and delete the A/ROSE extension. Reboot Basilisk II using the Special menu and you should be OK.

Thanks a lot! You saved my day :)
I noticed later that the solution was written in the error-message too, but I was to ignorant to even take a look at it.
Guess it's because I'm used to Windows error-messages, those ones only produces a blue-screen :)